1. Field of the Invention
The present invention relates to a torsion angle measuring method and device for measuring the torsion angle (or torsion angles in the roll direction and the pitch direction) of a magnetic-disk suspension which is a component part of a magnetic disk device, such as a hard disk drive.
2. Description of the Related Art
The method of measuring the torsion angle of a magnetic-disk suspension in the roll direction or the pitch direction is usually to measure the torsion angle of the slider surface (or the slider loading surface on which the slider is carried) to the suspension datum surface. Hereinafter, the torsion angle in the roll direction is called roll angle, and the torsion angle in the pitch direction is called pitch angle.
By using the measurement unit employing the laser displacement gage, the autocollimator, or the optical interference method, the angle measurement is carried out at the two places: the suspension datum surface and the slider loading surface. The measurement value is obtained by computing the difference between the two angles measured.
Moreover, there is also another method of measuring the torsion angle using the false lifted state of the suspension. In this method, the load pin whose loading edge is formed into the spherical surface comes in contact with the suspension at one point, so that the suspension is set in the false lifted state. And the torsion angle in the false lifted state of the suspension is measured. The false lifted state means the posture state of the suspension which imitates the actual state of the suspension where it is lifted from the magnetic disk surface when the magnetic head actually accesses the magnetic disk.
FIG. 5 is a flowchart for explaining the measurement procedure of the conventional torsion angle measuring method. FIG. 10 shows an example of the magnetic-disk suspension which is used as the measuring object.
As shown in FIG. 10, the suspension 1 comprises the datum surface 2 on the undersurface of the side (the right-hand side of FIG. 10) where the suspension 1 is attached to the magnetic disk device, and the slider loading surface at the leading edge of the opposite side (the left-hand side of FIG. 10) where the slider is carried. Moreover, the suspension 1 is provided with a predetermined position where the spherical-form edge of the load pin 8 comes in contact with the suspension 1 in performing the torsion angle measurement. Hereinafter, this predetermined position is called the reference position of the suspension for the load pin.
In the measurement procedure of FIG. 5, it is assumed that the fixture is provided so that the predetermined number of the suspensions (one lot) can be attached to the fixture, and that the torsion angles in the roll direction and the pitch direction for each of the suspensions on the fixture are measured continuously.
As shown in FIG. 5, the suspensions of the predetermined number (one lot) are attached to the fixture at step S11. The fixture is formed with a level criterion surface, and the plurality of suspensions are mounted on the criterion surface of the fixture at a time.
At step S12, the XY stage and the Z stage which are provided in the torsion angle measuring device are moved. The fixture and the plurality of suspensions on these stages are also moved.
At step S13, it is determined whether the movement to the measurement point of the suspension of concern (the measuring object) for measurement of the roll angle and pitch angle is completed. When the movement is not completed yet, control is returned to the step S12.
When the movement to the measurement point is completed, at step S14, the relative position of the load pin and the suspension is checked by the CCD image.
At step S15, the load pin is moved to the reference position of the suspension.
At step S16, it is determined whether the load pin is moved to the reference position of the suspension.
When the movement of the load pin is not completed yet, control is returned to the steps S14 and S15 so that movement of the load pin to the reference position of the suspension is performed again.
When the movement of the load pin is completed, at step S17, the roll angle “theta-r” and the pitch angle “theta-p” of the slider loading surface in the suspension to the datum surface are measured using the angle measuring instrument, and the measurement data is stored in the memory of the control unit (computer).
In the step S17, the angle measurement of the datum surface 2 of the suspension 1 fixed to the fixture and the angle measurement of the slider loading surface of the suspension 1 are performed, and the roll angle and the pitch angle are obtained by computing the difference of these angles as the torsion angle.
Therefore, when the torsion angles of the plurality of suspensions are measured, it is necessary to perform, for each of the plurality of suspensions, the positioning to move the load pin to the reference position of each suspension, the angle measurement of the datum surface 2, and the angle measurement of the slider loading surface.
At step S18, the measurement data “theta-r” of the roll angle and the measurement data “theta-p” of the pitch angle are displayed on the display monitor of the control unit.
At step S19, it is determined whether the measurement of the torsion angle is completed for all of the plurality of suspensions on the fixture.
When the result at step S19 is affirmative, control is shifted to the following step S21.
When the result at step S19 is negative, at step S20, control is shifted to the torsion angle measurement of the next suspension on the fixture, and the procedure of the steps S12 to S19 is repeated.
At step S21, the suspensions of the predetermined number (one lot) are detached from the fixture.
At step S22, it is determined whether the torsion angle measurement is finished for all the suspensions (all the lots).
When the result at step S22 is affirmative, the measurement procedure of FIG. 5 is terminated.
When the result at step S22 is negative, at step S23, control is shifted to the torsion angle measurement of the suspensions of the following lot, and the procedure of the steps S11 to S21 is repeated.
In recent years, with improvement of the recording density of the hard disk drive, a higher level of precision is demanded for the suspension machining. For this reason, the following problems arise: (1) the measurement process capability, and (2) the measurement error in the measurement using the false lifted state.
Concerning the measurement process capability, improvement in the throughput of the measuring devices must be aimed at. Although the quality of the torsion angle of the suspension was conventionally assured by the sampling inspection, it is now necessary to carry out the total inspection.
Concerning the measurement error in the measurement using the false lifted state, it is difficult to reduce the measurement error without decreasing the measurement process efficiency. In case the false lifted state is created by the load pin in the torsion angle measurement of the suspension, if the load pin in contact at the specified position (X, Y, Z coordinates) of the suspension is not-fixed, the posture state of the suspension will differ from the actual lifted state which is originally intended, and the torsion angle of the suspension in the wrong state will be measured so that the measurement error will be produced. Usually, in such a case, the measurement is performed after adjustment of the relative position between the load pin and the suspension is performed. However, worsening the measurement process efficiency is not avoided due to the time needed to perform the adjustment.